The Solar Orbiter (SolO)[7] is a Sun-observing probe developed by the European Space Agency (ESA) with a National Aeronautics and Space Administration (NASA) contribution. Solar Orbiter, designed to obtain detailed measurements of the inner heliosphere and the nascent solar wind, will also perform close observations of the polar regions of the Sun which is difficult to do from Earth. These observations are important in investigating how the Sun creates and controls its heliosphere.
SolO makes observations of the Sun from an eccentric orbit moving as close as ≈60 solar radii (RS), or 0.284 astronomical units (au), placing it inside Mercury's perihelion of 0.3075 au.[8] During the mission the orbital inclination will be raised to about 24°. The total mission cost is US$1.5 billion, counting both ESA and NASA contributions.[9]
SolO was launched on 10 February 2020 from Cape Canaveral, Florida (USA). The nominal mission is planned until the end of 2026, with a potential extension until 2030.
A comparison of the size of the Sun as seen from Earth (left, 1 au) and from the Solar Orbiter spacecraft (0.284 au, right)The Solar Orbiter structural thermal model shortly before leaving the Airbus Defence and Space facility in Stevenage, UK
Spacecraft
The Solar Orbiter spacecraft is a Sun-pointed, three-axis stabilised platform with a dedicated heat shield to provide protection from the high levels of solar flux near perihelion. The spacecraft provides a stable platform to accommodate the combination of remote-sensing and in situ instrumentation in an electromagnetically clean environment. The 21 sensors were configured on the spacecraft to allow each to conduct its in situ or remote-sensing experiments with both access to and protection from the solar environment. Solar Orbiter has inherited technology from previous missions, such as the solar arrays from the BepiColombo Mercury Planetary Orbiter (MPO). The solar arrays can be rotated about their longitudinal axis to avoid overheating when close to the Sun. A battery pack provides supplementary power at other points in the mission such as eclipse periods encountered during planetary flybys.
The Telemetry, Tracking and Command Subsystem provides the communication link capability with the Earth in X-band. The subsystem supports telemetry, telecommand and ranging. Low-Gain Antennas are used for Launch and Early Orbit Phase (LEOP) and now function as a back-up during the mission phase when steerable Medium- and High-Gain Antennas are in use. The High-Temperature High-Gain Antenna needs to point to a wide range of positions to achieve a link with the ground station and to be able to downlink sufficient volumes of data. Its design was adapted from the BepiColombo mission. The antenna can be folded in to gain protection from Solar Orbiter's heat shield if necessary. Most data will therefore initially be stored in on-board memory and sent back to Earth at the earliest possible opportunity.
The ground station at Malargüe (Argentina), with a 35-metre (115 ft) antenna, is used for 4 to 8 hours/day (effective). ESA's Malargüe ground station will be used for all operations throughout the mission with the ground stations in New Norcia, Australia, and Cebreros, Spain, acting as backup when necessary.[1]
Mission operations
Solar Orbiter · Mercury· Venus· Earth· Sun
During nominal science operations, science data is downlinked for eight hours during each communication period with the ground station. Additional eight-hour downlink passes are scheduled as needed to reach the required total science data return of the mission. The Solar Orbiter ground segment makes maximum reuse of ESA's infrastructure for Deep Space missions:
The ground stations, which belong to ESA's space tracking station network (ESTRACK)
The Mission Operations Centre (MOC), located at ESOC, Darmstadt, Germany
The communications network, linking the various remotely located centres and stations to support the operational data traffic
The Science Operations Centre was responsible for mission planning and the generation of payload operations requests to the MOC, as well as science data archiving. The SOC has been operational for the active science phase of the mission, i.e. from the beginning of the Cruise Phase onwards. The handover of payload operations from the MOC to the SOC is performed at the end of the Near-Earth Commissioning Phase (NECP). ESA's Malargüe Station in Argentina will be used for all operations throughout the mission, with the ground stations of New Norcia Station, Australia, and Cebreros Station, Spain, acting as backup when necessary.[10]
During the initial cruise phase, which lasted until November 2021, Solar Orbiter performed two gravity-assist manoeuvres around Venus and one around Earth to alter the spacecraft's trajectory, guiding it towards the innermost regions of the Solar System. At the same time, Solar Orbiter acquired in situ data to characterise and calibrate its remote-sensing instruments. The first close solar pass took place on 26 March 2022 at around a third of Earth's distance from the Sun.[11][12]
The spacecraft's orbit has been chosen to be 'in resonance' with Venus, which means that it will return to the planet's vicinity every few orbits and can again use the planet's gravity to alter or tilt its orbit. Initially, Solar Orbiter will be confined to the same plane as the planets, but each encounter of Venus will increase its orbital inclination. For example, after the 2025 Venus encounter, it will make its first solar pass at 17° inclination, increasing to 33° during a proposed mission extension phase, bringing even more of the polar regions into direct view.[11]
Scientific objectives
The spacecraft makes a close approach to the Sun every six months.[3] The closest approach will be positioned to allow a repeated study of the same region of the solar atmosphere. Solar Orbiter will be able to observe the magnetic activity building up in the atmosphere that can lead to powerful solar flares or eruptions.
Researchers also have the chance to coordinate observations with NASA's Parker Solar Probe mission (2018–2025) which is performing measurements of the Sun's extended corona, as well as other ground-based assets such as the Daniel K. Inouye Solar Telescope.
The objective of the mission is to perform close-up, high-resolution studies of the Sun and its inner heliosphere. The new understanding will help answer these questions:
How do solar transients drive heliospheric variability?
How do solar eruptions produce energetic particle radiation that fills the heliosphere?
How does the solar dynamo work and drive connections between the Sun and the heliosphere?
Science results
Since the launch of the mission, a series of papers have been released in three special issues of the Astronomy and Astrophysics Journal:
The Solar Orbiter mission
Solar Orbiter First Results (Cruise Phase)
Solar Orbiter First Results (Nominal Mission Phase)
Meanwhile, regular "science nuggets" are released on the Solar Orbiter science community website.
Instruments
The science payload is composed of 10 instruments:[13]
Heliospheric in-situ instruments (4)
SWA – Solar Wind Plasma Analyser (United Kingdom): Consists of a suite of sensors that measures the ion and electron bulk properties (including density, velocity, and temperature) of the solar wind, thereby characterizing the solar wind between 0.28 and 1.4 au from the Sun. In addition to determining the bulk properties of the wind, SWA provides measurements of solar wind ion composition for key elements (e.g. the C, N, O group and Fe, Si or Mg)[4][14]
EPD – Energetic Particle Detector (Spain): Measures the composition, timing and distribution functions of suprathermal and energetic particles. Scientific topics to be addressed include the sources, acceleration mechanisms, and transport processes of these particles[4]
MAG – Magnetometer (United Kingdom): Provides in situ measurements of the heliospheric magnetic field (up to 64Hz) with high precision. This will facilitate detailed studies into the way the Sun's magnetic field links into space and evolves over the solar cycle; how particles are accelerated and propagate around the Solar System, including to the Earth; how the corona and solar wind are heated and accelerated[4]
RPW – Radio and Plasma Waves (France): Unique amongst the Solar Orbiter instruments, RPW makes both in situ and remote-sensing measurements. RPW measures magnetic and electric fields at high time resolution using a number of sensors/antennas, to determine the characteristics of electromagnetic and electrostatic waves in the solar wind[4]
Solar remote-sensing instruments (6)
PHI – Polarimetric and Helioseismic Imager (Germany): Provides high-resolution and full-disk measurements of the photospheric vector magnetic field and line-of-sight (LOS) velocity as well as the continuum intensity in the visible wavelength range. The LOS velocity maps have the accuracy and stability to allow detailed helioseismic investigations of the solar interior, in particular of the solar convection zone high-resolution and full-disk measurements of the photospheric magnetic field[4]
EUI – Extreme Ultraviolet Imager (Belgium): Images the solar atmospheric layers above the photosphere, thereby providing an indispensable link between the solar surface and outer corona that ultimately shapes the characteristics of the interplanetary medium. Also, EUI provides the first-ever UV images of the Sun from an out-of-ecliptic viewpoint (up to 33° of solar latitude during the extended mission phase)[4]
SPICE – Spectral Imaging of the Coronal Environment (France): Performs extreme ultraviolet imaging spectroscopy to remotely characterize plasma properties of the Sun's on-disk corona. This will enable matching in situ composition signatures of solar wind streams to their source regions on the Sun's surface[4][15][16]
STIX – Spectrometer Telescope for Imaging X-rays (Switzerland): Provides imaging spectroscopy of solar thermal and non-thermal X-ray emission from 4 to 150 keV. STIX provides quantitative information on the timing, location, intensity, and spectra of accelerated electrons as well as of high-temperature thermal plasmas, mostly associated with flares and/or microflares[4]
Metis[17] – Coronagraph (Italy): Simultaneously images the visible and far ultraviolet emissions of the solar corona and diagnoses, with unprecedented temporal coverage and spatial resolution, the structure and dynamics of the full corona in the range from 1.4 to 3.0 (from 1.7 to 4.1) solar radii from Sun centre, at minimum (maximum) perihelion during the nominal mission. This is a region that is crucial in linking the solar atmospheric phenomena to their evolution in the inner heliosphere[4]
SoloHI – Solar Orbiter Heliospheric Imager (United States): Images both the quasi-steady flow and transient disturbances in the solar wind over a wide field of view by observing visible sunlight scattered by solar wind electrons. SoloHI provides unique measurements to pinpoint coronal mass ejections (CMEs). (NRL provided)[4][18]
Institutions involved
Solar Orbiter spacecraft is prepared for encapsulation in the United Launch Alliance Atlas V payload fairing.
The following institutions operate each instrument:[19]
The launch of Solar Orbiter from Cape Canaveral at 11.03pm EST on 9 February 2020 (US date)
In April 2015, the launch was set back from July 2017 to October 2018.[21] In August 2017, Solar Orbiter was considered "on track" for a launch in February 2019.[22] The launch occurred on 10 February 2020[5] on an Atlas V 411.[23]
Launch
The Atlas V 411 (AV-087) lifted off from SLC-41 at Cape Canaveral, Florida, at 04:03 UTC. The Solar Orbiter spacecraft separated from the Centaur upper stage nearly 53 minutes later, and the European Space Agency acquired the first signals from the spacecraft a few minutes later.[9]
Trajectory
After launch, Solar Orbiter will take approximately 3.5 years, using repeated gravity assists from Earth and Venus, to reach its operational orbit, an elliptical orbit with perihelion 0.28 AU and aphelion 0.91 AU. The first flyby was of Venus in December 2020. Over the expected mission duration of 7 years, it will use additional gravity assists from Venus to raise its inclination from 0° to 24°, allowing it a better view of the Sun's poles. If an extended mission is approved, the inclination could rise further to 33°.[1][24]
During its cruise phase to Venus, Solar Orbiter passed through the ion tail of Comet C/2019 Y4 (ATLAS) from 31 May to 1 June 2020. It passed through the comet's dust tail on 6 June 2020.[25][26]
In June 2020, Solar Orbiter came within 77,000,000 km (48,000,000 mi) of the Sun, and captured the closest pictures of the Sun ever taken.[27]
Mission timeline
The speed of the probe and distance from the Sun
April 2012: €319 million contract to build orbiter awarded to Astrium UK[28]
June 2014: Solar shield completes 2 week bake test[29]
September 2018: Spacecraft is shipped to IABG in Germany to begin the environmental test campaign[30]
Solar Orbiter and Parker Solar Probe collaboration
In 2022, SolO and NASA's Parker Solar Probe (PSP) collaborated to study why the Sun's atmosphere is "150 times hotter" than its surface. SolO observed the Sun from 140 million kilometers, with PSP simultaneously observed the Sun's corona during flyby at a distance of nearly 9 million kilometers.[36][37]
In March 2024, both space probes are at their closest approach to the Sun, PSP at 7.3 million km, and SolO at 45 million km. SolO observed the Sun, while PSP sampled the plasma of solar wind, that allowed scientists to compare data from both probes.[38]
Outreach
Solar Orbiter news are regularly updated and listed in the official ESA public pages , as well as on the Twitter/X account .
Images taken by the spacecraft with various instruments can be found on the official Flickr account.
^ ab"GMS: Solar Orbiter's Orbit". svs.gsfc.nasa.gov. 27 January 2020. Retrieved 14 February 2020. This article incorporates text from this source, which is in the public domain.
^"Solar Orbiter crosses the Earth-Sun line as it heads for the Sun". esa.int. Retrieved 30 March 2022.
^Owen, C. J.; et al. (October 2020). "The Solar Orbiter Solar Wind Analyser (SWA) suite". Astronomy & Astrophysics. 642: A16. Bibcode:2020A&A...642A..16O. doi:10.1051/0004-6361/201937259. S2CID 224966409.
^"SPICE on Solar Orbiter official website". spice.ias.u-psud.fr. 12 November 2019. Retrieved 12 November 2019.
^"SPICE - Spectral Imaging of the Coronal Environment". Archived from the original on 11 May 2011. Retrieved 11 May 2011.
^"Metis: the multi-wavelength coronagraph for the Solar Orbiter mission". Retrieved 29 January 2021.
^"Solar Orbiter Heliospheric Imager (SoloHI) – Space Science Division". Nrl.navy.mil. Archived from the original on 9 August 2018. Retrieved 9 August 2018.
^"Solar Orbiter: Mission zur Sonne und inneren Heliosphäre". www.mps.mpg.de.
^Leibniz-Institut für Astrophysik Potsdam. "Solar Orbiter (SolO)". Webseite.
^"ESA Science & Technology - Solar Orbiter launch moved to 2018". sci.esa.int.
^"Europe's Solar Orbiter on track for 2019 launch". Air & Cosmos. 28 August 2017. Retrieved 19 September 2017.
^"Solar Orbiter: Summary". ESA. 20 September 2018. Retrieved 19 December 2018.
^"ESA Science & Technology: Summar". Sci.esa.inty. 28 February 2018. Retrieved 20 March 2018.
^ ab"Solar Orbiter to pass through the tails of Comet ATLAS". 29 May 2020. Retrieved 1 June 2020.
^ abWood, Anthony (29 May 2020). "ESA'S Solar Orbiter set for unexpected rendezvous with Comet ATLAS". New Atlas. Retrieved 1 June 2020.
^"Solar Orbiter's first images reveal 'campfires' on the Sun". ESA. 16 July 2020. Retrieved 23 January 2021.
^"ESA contracts Astrium UK to build Solar Orbiter". Sci.esa.int. April 2012.
^"Solar Orbiter's shield takes Sun's heat". Esa.int. June 2014.
^Amos, Jonathan (18 September 2018). "Solar Orbiter: Spacecraft to leave UK bound for the Sun". BBC News.
^Thompson, Amy (10 February 2020). "Solar Orbiter launches on historic mission to study the sun's poles". space.com. Retrieved 10 February 2020.
^Hatfield, Miles (15 July 2020). "Solar Orbiter Returns First Data, Snaps Closest Pictures of the Sun". NASA. Retrieved 15 January 2021.
^"Solar Orbiter Spacecraft Catches a Second Comet by the Tail". 27 January 2022. Retrieved 1 August 2023.
^"Zooming into the Sun with Solar Orbiter". www.esa.int. Retrieved 29 March 2022.
^"Solar Orbiter solves magnetic switchback mystery". www.esa.int. Retrieved 24 December 2022.
^Skibba, Ramin. "A Pair of Sun Probes Just Got Closer to Solving a Solar Enigma". Wired. Archived from the original on 20 September 2023. Retrieved 30 March 2024.
^Telloni, Daniele; et al. (1 September 2023). "Coronal Heating Rate in the Slow Solar Wind". The Astrophysical Journal Letters. 955 (1): L4. arXiv:2306.10819. Bibcode:2023ApJ...955L...4T. doi:10.3847/2041-8213/ace112.
^"ESA and NASA team up to study solar wind". www.esa.int. Retrieved 30 March 2024.
External links
Wikimedia Commons has media related to Solar Orbiter.
New ESA Solar Orbiter homepage (from December 2020)
Launches are separated by dots ( • ), payloads by commas ( , ), multiple names for the same satellite by slashes ( / ). Cubesats are smaller. Crewed flights are underlined. Launch failures are marked with the † sign. Payloads deployed from other spacecraft are (enclosed in parentheses).
